Summer is here, and with it come long, hot days outside. But as temperatures and humidity go up, so does the risk of heat-related illness. Sweating heavily without replacing enough fluids can lead to dehydration or heat cramps. If the body cannot shed enough heat for any reason, there is a risk of heat exhaustion and, in extreme cases, heat stroke - a medical emergency.

Children are particularly vulnerable to heat-related illnesses, because their bodies do not get rid of heat as efficiently as adults' do. To help ensure a safe, healthy summer, make sure you know how to prevent, recognize, and treat heat-related illness.

About heat-related illness

Dehydration

Children can become dehydrated when they lose more body fluid by sweating or urinating than they replace by drinking. Even a small amount of dehydration, amounting to just 2% of body weight, can affect a child. Dehydration also increases the risk of other heat-related illnesses, because it interferes with the body's ability to regulate temperature.

Symptoms of dehydration include:

dry or sticky mouth

thirst

low or no urine output; concentrated urine appears dark yellow

not producing tears

being irritable or cranky

seeming bored or uninterested

headache

dizziness

cramps

chills

fatigue

In severe cases, dehydration can cause:

sunken eyes

sunken soft spot, or fontanelle, on the top of the head in an infant

nausea or vomiting

lethargy or coma

If you suspect your child is dehydrated, move him to a cool, shady area and give him plenty of water, clear juice, or a sports drink. If he does not feel better soon, take him to see a doctor. If he is unconscious or unresponsive, do not wait; take him to see a doctor right away.

Hyponatremia

If a child drinks more water than he needs to replace lost fluid or if he loses large amounts of salt in sweat, this may cause a low blood sodium level, known as hyponatremia. This condition is quite rare but can be dangerous.

Hyponatremia is more likely to happen if a child:

does not usually get enough salt in his diet

loses large amounts of salt during strenuous or prolonged exercise

drinks much more water than he needs during or after exercise

To prevent hyponatremia, it is important to replace both lost water and lost salt, either with a sports drink or a meal.

Heat cramps

Heat cramps usually happen during or after exercise when a child has lost large amounts of fluid and salt in sweat.

Symptoms of heat cramps include:

intense muscle pain, which is not caused by injury, in the arms, legs, or abdomen

muscle spasms that continue during or after exercise

If your child has heat cramps, he should stop exercising and sit down. Give your child clear juice or a sports drink to help replace fluid and salt. Light stretching, relaxation, and massage may also help. Your child should not exercise for a few hours after the cramps stop.

If the cramps do not go away after an hour, take your child to a doctor.

Heat exhaustion

Heat exhaustion is caused by loss of water and salt, often as a result of exercise in hot weather. If it is not treated, it may progress to heat stroke.

Symptoms of heat exhaustion include:

normal or elevated body temperature, although not as high as 40°C (104°F)

profuse sweating

pale skin

skin may be cool and moist

fast, shallow breathing

fast, weak pulse

headache

nausea, vomiting, or diarrhea

dizziness, weakness, or fainting

heat cramps

exhaustion

If your child has any of these symptoms, move him to a shady or air-conditioned area and have him lie comfortably. Remove extra clothing and sports equipment, if any. Cool him with cold water, fans, or cold towels. If he is not nauseated or vomiting, have him drink chilled water, juice, or a sports drink.

The child's condition should improve quickly. If he does not seem better after an hour, take him to a doctor.

If his symptoms are severe, or if he seems confused or disoriented or is behaving oddly, take him to a doctor right away.

Heat stroke

Heat stroke is a dangerous illness that can lead to organ damage or death. Heat stroke happens when a child's body creates more heat than it can release. The child's core body temperature increases rapidly, to 40° C or higher.

The main signs of heat stroke are:

increase in core body temperature, usually above 40° C (104° F)

central nervous system dysfunction, which may take the form of altered consciousness, seizures, confusion, emotional instability, or irrational behaviour

Other possible signs of heat stroke include:

nausea, vomiting, or diarrhea

headache

dizziness or weakness

hot and wet or dry skin

increased heart rate

fast breathing

Heat stroke is a medical emergency. Call 911/emergency medical services right away. Remove the child's clothing and any sports equipment. Begin cooling the child by any means available, including immersing him in cold water, spraying him with cold water, fans, or ice bags. Monitor the child's body temperature. Do not give the child anything to drink. If emergency services do not arrive quickly, call again for instructions.

How the body controls temperature

To work properly, our bodies need to maintain a core temperature of about 37° C at all times. Body temperature is tightly controlled by a "thermostat" in a part of the brain called the hypothalamus. When the body's core temperature rises above its "set point," the hypothalamus turns on various heat loss mechanisms, including faster, shallower breathing; increased blood flow to the skin; and sweating.

In humans, most excess heat is shed through the skin. Blood brings heat from the core body tissues to the skin. Heat then passes from the skin to the environment through:

conduction: heat passes from the skin to a cooler object

convection: cooler air currents remove heat from the skin

radiation: the skin emits small amounts of radiant energy

evaporation: body heat is used to turn sweat into water vapour

If the surrounding air is cool and dry, it is easy for the body to get rid of heat. The hotter and more humid it gets, though, the more difficult it becomes to get rid of heat:

If the air is as hot as or hotter than the skin, about 36°C, the body will absorb heat from its surroundings. The only cooling mechanism that still works is evaporation.

If a person stands in direct sunlight, especially if wearing dark clothing, the body will absorb heat from the sun.

If the air is also very humid, evaporation no longer works well. As a result, we sweat heavily, but do not lose much heat.

In other words, high temperatures, high humidity, and direct sunlight all make the body work harder to get rid of excess heat.

Who is at risk for heat-related illness?

For proper temperature regulation, especially in hot or humid conditions, we need healthy skin, good blood flow to the skin, enough fluid in our bodies, and a properly functioning hypothalamus. Anyone whose body has trouble with temperature regulation or who cannot escape the heat is at risk when the temperature rises. These include:

babies and young children, who do not regulate temperature as well as older children and adults: the surface area of their bodies is high relative to their body mass so they absorb more heat from the environment, they produce more heat when exercising, they sweat less than adults, and they may forget or not know to drink plenty of fluids

children with mental retardation, who may not recognize the need to replace fluid loss

children who cannot move or change position by themselves

children with chronic illnesses such as diabetes, cystic fibrosis, or heart conditions

children with acute illnesses, including fever, gastrointestinal infection, or sunburn

children who exercise heavily, especially if they are not used to the heat, not very fit, or obese

children who are taking certain drugs that reduce the body's ability to regulate its temperature, such as antihistamines, diuretics, or drugs for mental health conditions; check with your doctor or pharmacist if you or your child take medication regularly

any child who has had heat-related illness in the past

Staying cool and preventing heat-related illness

Heat-related illness can be avoided by taking the right precautions.

In Canada, temperature and humidity readings are often combined into a humidex reading, a rough description of how hot it actually feels. While the humidex is not a perfect tool, you can use the humidex forecast for the day to plan ahead.

Humidex readings and comfort levels (Environment Canada)

Less than 29° C (84° F): No discomfort

30°C to 39°C (86°F to 102°F): Some discomfort

40°C to 45°C (104°F to 113°F)L Great discomfort; avoid exertion

Above 45°C (113°F): Dangerous

Above 54°C (129°F): Heat stroke imminent

To stay cool:

Limit outdoor activities.

Stay out of direct sunlight and crowded areas.

Rest often in shady areas, or go to an air-conditioned space.

Drink non-alcoholic, non-diuretic fluids. Water is a good option, but children may drink more of a flavoured beverage such as juice or a sports drink.

Be aware that fans only move the air around; they do not cool it. Fans work best in front of an open window.

Never leave children or pets alone in a car, even for a few minutes.

Sports and exercise in the heat

Sports are an important part of summer for many children and teens. However, it's important to avoid heat-related illness. Children who exercise in the heat are at higher risk than adults, because they produce more heat, sweat less, and may forget to drink enough.

If your child is going to be exercising or playing sports:

Make sure the coach or supervisor is knowledgeable about exercising in the heat and that there is a plan for dealing with heat-related illnesses if they arise.

Reduce the intensity of exercise when it is very hot, humid, or sunny.

Take frequent breaks.

Wear lightweight, light-coloured, loose-fitting clothing.

Make sure children are well hydrated before exercising.

Make sure children drink every 15 to 20 minutes when exercising, even if they don't feel thirsty. One way to tell whether your child is drinking enough is to weigh him before and after the activity, wearing very little clothing. If he weighs less after the activity than before, he is not drinking enough. However, if he weighs more after the activity, he is drinking too much.

Don't use salt tablets to replace electrolytes, as they provide too much salt.

If it is very hot and humid, cancel the activity or move to an air-conditioned space.

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